Importance

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Abstract

A fingerprint sensor includes a plurality of semiconductor devices adjacent a substrate and defining active circuit portions, and having only three metal layers. More particularly, the sensor may include a first metal layer interconnecting predetermined ones of the plurality of semiconductor devices; a second metal layer defining a ground plane; and a third metal layer comprising an array of electric field sensing electrodes connected to active circuit portions for generating an output related to a sensed fingerprint. The fingerprint sensor may also include a package surrounding the substrate and having an opening aligned with the sensing electrodes. In addition, a first external electrode may be carried by the package for contact by a finger. The sensor may thus also include an excitation drive circuit connected between the ground plane and the first external electrode for generating electric fields between the electric field sensing electrodes and adjacent finger portions. A power control circuit is for controlling operation of active circuit portions based upon sensing finger contact with the first external electrode so that the active circuit portions are powered upon sensing finger contact with the first external electrode and otherwise grounded. A second external electrode may be connected to a bleed resistor to bleed charge from the finger prior to switching from the grounded to the powered state. An amplifier connected between each electric field sensing electrode and associated shield electrode may be operated at a gain of greater than one for additional noise rejection.

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First Claim